I have been running CS4 with no problems for over a month. As of a few days ago, when I lauch CS4, I get the beachball. I force a quit, relaunch and all is well. When I quit from that successful relaunch, I get a warning that Photoshop quit unexpectedly--of course, from my point of view there was nothing unexpected about it. I have run Onyx, restarted etc. I have read the report but it means nothing to me:

I have recently installed the trial version of Nik Effects--this is the only new thing I can think of. I have full backups (both Time Machine and Super Duper).

Can anyone give me a clue what I should do? Reinstall CS4? Delete Nik Effects? As of now, it works, I just have to lauch twice and put up with the erroneous quit warning but I would like to get to the bottom of this.

your instincts were correct. I have removed Nik effects and there is no problem. Thank you (even if it wasn't the answer I wanted). Now I will write to them. Their website states it is CS4 compatible with Macs but I am wondering if they need to tweak it. I have my heart set on buying this, wish it was an "easy purchase", ha! Again, thank you for the nudge in the right direction.